In recent years, mobile devices (electronic devices, more specifically, portable electronic devices), which include a screen (e.g. a liquid crystal screen) having a touch panel, have been widely used. Mobile phones and smart phones are typical examples of such mobile devices. The mobile devices are in the process of increasingly becoming more multi-functioned, more compact, or thinner. Some of the mobile devices, recently put on the market, are equipped with a proximity sensor. The proximity sensor detects (senses) whether or not there is an object which comes close to a mobile device in which the proximity sensor is included.
The proximity sensor is applied, for example, to the following case. Specifically, a user holds his phone, which includes a screen having a touch panel, to his ear when the user answers a call. The phone may erroneously operates if the screen is accidentally brought into contact with his skin while he is holding the phone to his ear in a situation where (i) a screen display is ON and (ii) a touch panel function is activated.
To prevent such an erroneous operation, the following control is carried out. In a case where the proximity sensor detects the user's skin that comes close to the phone while the phone is being held to his ear in a situation where (i) the screen display is ON and (ii) the touch panel function is activated, a control section of the phone carries out the following control in accordance with a result detected by the proximity sensor.
The control section controls the display screen to be turned off and the touch panel function to be changed from an active state to a non-active state. And, when the phone is taken away from the user's skin after he finishes talking on the phone, the proximity sensor detects a change from (i) a proximity state in which the skin comes close to the phone to (ii) a non-proximity state in which the skin does not come close to the phone. In response to the change thus detected by the proximity sensor, the control section controls the screen display to be turned on again and the touch panel function to be activated again.
Next, the following description will discuss a case where a proximity sensor is used in a media player, which is a mobile device. Before getting into the main topic, we will briefly describe a media player in which no proximity sensor is mounted. Normally, a user presses a button in order to turn off a power source of a panel in the media player, in which no proximity sensor is mounted. The panel is turned off when, for example, the media player is in a pocket of the user.
Now, the following description will discuss a media player in which a proximity sensor is mounted. In a case where (i) the media player is put into a user's pocket in a situation where (a) a screen display is ON and (b) a touch panel function is activated and (ii) the proximity sensor detects a state where the media player and a material of clothes that the user is wearing (or a material of the user's pocket) are in proximity with each other in the user's pocket, the screen display of the media player is controlled to be turned off and the touch panel function of the media player is changed to a non-active state.
In contrast, in a case where the media player is taken out the user's pocket and the proximity sensor detects a state where the media player and the material of the clothes (or the material of the user's pocket) are not in proximity to each other, the screen display of the media player is controlled to be turned on again and the touch panel function of the media player is controlled to be changed to an active state again.
Since the screen display and the touch panel function are thus controlled, it becomes possible to prevent a mobile device from erroneously operating in a case where a touch panel function is in an active state during a time period not intended by the user. In addition, since the screen display is controlled to be turned off, it becomes also possible to reduce power consumption.
It is anticipated that a proximity sensor will be generally employed in various electronic devices such as mobile phones and media players. Note that conditions (i.e., conditions for mounting the proximity sensor) such as (i) where in an electronic device the proximity sensor is to be mounted and (ii) a shape of an outer surface of a housing of the electronic device in which the proximity sensor is mounted vary among makers and product models. This is mainly because the conditions are bound by a physical appearance of and a design of an electronic device in which the proximity sensor is to be mounted. Such being the case, there is a big demand for a proximity sensor (object sensing device) whose property is equal among various mounting conditions. Note that indices of the property encompass a detection distance (a distance, between an object to be detected and the proximity sensor, which causes the proximity sensor to determine that the object to be detected comes close to the electronic device) and a rate of occurrence of erroneous operations.
Patent Literature 1 and 2 disclose conventional proximity sensors. Patent Literature 1 discloses a proximity sensor which has an illuminance sensing function and can reduce power consumption without deteriorating accuracy in detecting a proximity state of an object to be detected. Patent Literature 2 discloses a mobile phone 1 that includes a human sensor 10 for determining whether or not a person comes close to the mobile phone 1, on the basis of a signal supplied from an infrared sensor and a signal supplied from a proximity sensor.
FIG. 6 is a block diagram illustrating a conventional proximity sensor 101, which is configured by main parts of the proximity sensor, disclosed in Patent Literature 1, which has the illuminance sensing function.
The proximity sensor 101 illustrated in FIG. 6 is mounted in an electronic device. The proximity sensor 101 includes a light-emitting element 102, a light-receiving element 103, a determination section 104, and a control section 105. The light-emitting element 102 projects (emits), toward a predetermined space, light 106. The light-receiving element 103 receives reflected light 107, which is light obtained when the light 106 is reflected from an object B to be detected to which object B a detection of whether or not the object B to be detected comes close to the proximity sensor 101 is carried out. The light-receiving element 103 supplies an electric current signal S103 in accordance with a quantity of the reflected light 107. The determination section 104 includes a first electric current source that supplies a predetermined first threshold electric current and a second electric current source that supplies a predetermined second threshold electric current. The determination section 104 determines whether the electric current signal S103 is not more than the second threshold electric current or more than the first threshold electric current. The determination section 104 supplies a determination result signal S104 indicative of a result of determination made by the determination section 104. The control section 105 supplies, to the light-emitting element 102, a light emission instruction signal S102 for instructing the light-emitting element 102 to project the light 106. In a case where the electric current signal S103 is not more than the second threshold electric current, the control section 105 determines that the proximity sensor 101 is in a non-proximity state, in which the object B to be detected does not come close to the proximity sensor 101. In a case where the electric current signal S103 is more than the first threshold electric current, the control section 105 determines that the proximity sensor 101 is in a proximity state, in which the object B to be detected comes close to the proximity sensor 101. Then, the control section 105 supplies, to the electronic device, a signal S106 indicative of the non-proximity state (or the proximity state) and for controlling the electronic device. Note that a signal S101 can be externally supplied to the control section 105 if necessary.
The light-emitting element 102 and the light-receiving element 103, each molded with molding resin, are provided in a single package. In some of the proximity sensors currently on the market, the light-emitting element 102 and the light-receiving element 103 are separately provided instead of being provided in a single package.
The following description will discuss a principle of operation of the proximity sensor 101 illustrated in FIG. 6. According to the proximity sensor 101, the light 106, projected from the light-emitting element 102 toward the predetermined space, is reflected from the object B to be detected and then enters, as the reflected light 107, the light-receiving element 103.
The determination section 104 includes the first and second electric current sources that supply the predetermined first and second threshold electric currents, respectively. The determination section 104 makes a comparison between the electric current signal S103 and the respective predetermined first and second threshold electric currents so as to determine (judge) whether the electric current signal S103 is more than the predetermined first threshold electric current or not more than the predetermined second threshold electric current. A result of the determination is supplied, as the determination result signal S104, to the control section 105. Thus, a state, indicating whether or not the object B to be detected comes close to the proximity sensor 101, is determined. The following description will discuss this in detail.
In a case where the object B to be detected does not come close to the proximity sensor 101, the light 106, which is projected from the light-emitting element 102 in response to the light emission instruction signal S102 supplied from the control section 105, is diffused. As a result, little of the reflected light 107 enters the light-receiving element 103.
This causes the determination section 104 of the proximity sensor 101 to determine that the electric current signal S103 is not more than the predetermined second threshold current. The determination section 104 supplies, to the control section 105, the determination result signal S104 indicating that the electric current signal S103 is not more than the predetermined second threshold electric current. This causes the proximity sensor 101 to be changed to the non-proximity state (the state in which the object B to be detected does not come close to the proximity sensor 101).
In contrast, in a case where the object B to be detected comes close to the proximity sensor 101, the light 106, which is projected from the light-emitting element 102 in response to the light emission instruction signal S102 supplied from the control section 105, is reflected from the object B to be detected and then enters, as the reflected light 107, the light-receiving element 103.
The determination section 104 of the proximity sensor 101 determines that the electric current signal S103 is more than the predetermined first threshold current. The determination section 104 supplies, to the control section 105, the determination result signal S104 indicating that the electric current signal S103 is more than the predetermined first threshold electric current. This causes the proximity sensor 101 to be changed to the proximity state (the state in which the object B to be detected comes close to the proximity sensor 101).